12 JavaScript quirks

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A core of JavaScript (the so-called “good parts”) is elegant, but that core is often obscured by quirks. This introduction is the first of a series of blog posts that looks at twelve common quirks and how to best deal with them:


  1. Implicit conversion of values

  2. Two “non-values” – undefined and null

  3. Normal equality (==)

  4. Unknown variable names create global variables

  5. Parameter handling

  6. The scope of variables

  7. Inadvertent sharing of variables via closures

  8. Array-like objects

  9. Subtyping constructors

  10. Reading and writing of properties

  11. this in real functions

  12. The for-in loop


A concluding post will cover ECMAScript 6 [1], which will eliminate most of the above quirks.


The series will provide a good overview of JavaScript. It is a translation of a previous blog post in German.
ECMAScript 5 will be used and a basic knowledge of JavaScript is required, but much will be explained. I will post one quirk per week.


Reference:


  1. ECMAScript: ES.next versus ES 6 versus ES Harmony


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